---
name: "a64l"
section: "3"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/a64l"
---

# a64l(3)

convert between long and base-64

## NAME

a64l, l64a - convert between long and base-64

## LIBRARY

Standard C library (*libc*, *-lc*)

## SYNOPSIS

```
#include <stdlib.h>
```

**long a64l(const char \****str64***);** **char \*l64a(long** *value***);**

Feature Test Macro Requirements for glibc (see [**feature\_test\_macros**(7)](/feature_test_macros/7.md)):

**a64l**(), **l64a**():

```
    _XOPEN_SOURCE >= 500
        || /* glibc >= 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _SVID_SOURCE
```

## DESCRIPTION

These functions provide a conversion between 32-bit long integers and little-endian base-64 ASCII strings (of length zero to six). If the string used as argument for **a64l**() has length greater than six, only the first six bytes are used. If the type *long* has more than 32 bits, then **l64a**() uses only the low order 32 bits of *value*, and **a64l**() sign-extends its 32-bit result.

The 64 digits in the base-64 system are:

```
'.'	represents a 0
'/'	represents a 1
0-9	represent  2-11
A-Z	represent 12-37
a-z	represent 38-63
```

So 123 = 59\*64^0 + 1\*64^1 = "v/".

## ATTRIBUTES

For an explanation of the terms used in this section, see [**attributes**(7)](/attributes/7.md).

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **l64a**() | Thread safety | MT-Unsafe race:l64a |
| **a64l**() | Thread safety | MT-Safe |

## STANDARDS

POSIX.1-2008.

## HISTORY

POSIX.1-2001.

## NOTES

The value returned by **l64a**() may be a pointer to a static buffer, possibly overwritten by later calls.

The behavior of **l64a**() is undefined when *value* is negative. If *value* is zero, it returns an empty string.

These functions are broken before glibc 2.2.5 (puts most significant digit first).

This is not the encoding used by [**uuencode**(1)](/uuencode/1.md).

## SEE ALSO

[**uuencode**(1)](/uuencode/1.md), [**strtoul**(3)](/strtoul/3.md)